css - Able to set width % but not height -

I am making a beginning in CSS, and I have tried to find the answer but I could not find it. So please bear with me: D

I have a code that is in my code (because it is a responsive mobile web), I will show it in the case related to my problem: < Pre> & lt; Meta name = "viewport" content = "width = device-width, initial-level = 1.0, maximum-scale = 1.0, minimum-scale = 1.0, user-scalable = 0" & gt;

This is a part of my code, where I want to change the img width and height With:

  & lt; Div id = "desc" & gt; & Lt; Img alt = "src =" picture / MallDetail / MallDesc.png "& gt; & Lt; / Div & gt;   
 So I tried to do something like this:  
  #desc img {float: left; Width: 95%; Height: 50%; Margin: 0 2.5% 0 2.5%; }   
 Then there was a strange thing: the width is working perfectly, the  img   width  size is 95% of the current width , But  height  is not working - it is not currently changing (its  height  should be 50% of the current height).  
 I have  margin 0  and  padding 0  to reset my CSS.  
 Why is this happening? What should I do to work?   
  
  
 
 P> You can not set the height by using% Width increases when using% for height width.  
 You should use the minimum height: 90px; Then the height inside the material increases.  
 For example.  
  & lt; Div id = "mainContainer" & gt; & Lt; Img src = "helloword" alt = "style =" width: 100% "/> & Lt; Div class "newcontent" & gt; & Lt; H1 & gt; Hello & lt; / H1> & Lt; / Div & gt; & Lt; / Div & gt;   
 CSS:  
  #mainContainer {min-height: 80px; Width: 100%; }